The three major problems which are being studied in this project are (1) Studies on the correlation of ultrastructural and biochemical events in insulin secretion of beta cells using isolated islets and monolayer cultures of islet cells maintained in vitro. (2) Studies on the transplantation of isolated islets via portal vein injection (3). Studies on the formation, storage and release of insulin in human islets maintained in vitro. Monolayer culture of islet cells will be used to continue studies on the role of the microtubular and microfilament system in insulin secretion. Alloxan is being used as a possible probe for establishing the presence of a gluco-receptor-transport site on the membrane of the beta cell utilizing the perifusion system for in vitro studies on insulin secretion. The protective effect of glucose and other agents against the in vitro inhibitory effect of alloxan on glucose-induced insulin secretion will be continued as well as studies on the effect of certain proteolytic enzymes on glucose-induced insulin secretion in the perifused islets. The site of localization and ultimate fate of the alpha, beta and D cell in normal islets transplanted into the liver by portal vein injection into the Lewis strain of rats with experimental diabetes will be continued. Studies will also be accomplished on injection of allografts of isolated islets via the portal vein and the effect of in vitro culture of isolated islets prior to transplantation. Normal human islets have been isolated and maintained in vitro thus in vitro studies will be continued on the formation, storage and release of insulin in normal human islets utilizing the facilities of the Clinical Unit for Recent Expirations (CURE) to obtain the islets as rapidly as possible after expiration.